This application claims benefit of Japanese Patent Application No. 2001-139558 filed on May 10, 2001, the contents of which are incorporated by the reference.
The present invention relates to disk devices and, more particularly, to a disk device having a cache memory for provisionally holding predetermined data read out into and stored in its storing medium.
A prior art disk device using a magnetic disk or the like as storing medium has a cache memory (or disk cache) for improving the access performance. The cache memory is a fast accessible memory for provisionally storing data to be written in the storing medium of the disk device or data read out from the storing medium in response to a command from an upper rank host.
Up to date, in databases or OSs (operating systems) data stored in a particular area is referred to as index or table, and it is thus demanded to be able to fast access the area, in which such index or the like has been stored.
To meet this demand, a method is adopted, in which index or table is held as steadily available data in a semiconductor disk or a main memory provided in a personal computer. In an alternative method that is adopted, it is determined that it is highly possible that index is held in a particular area (i.e., young address area) of a magnetic disk device (i.e., storing medium itself), and this area is held as steadily available area in a cache memory of the disk device.
In the former method, however, it is necessary to add predetermined semiconductor memory or main memory to the personal computer body, thus leading to additional expenditures. In the latter method, index of database or the like may not always be held in a young address area. Therefore, it is not always possible to fast access the index.